Harmonic producer



y 1938- L. R. WRATHALL 2,117,752

HARMONIC PRODUCER Filed May 5, 1956 2 Sheets-Sheet 1 FIG. 2

El/f/VHARMO/V/C FILTER BANK /'/vv/v 70/? L. R. WRATHALL ATTORNEY May 17, 1938. 1.. R. WRATHALL HARMONIC PRODUCER 2 Sheet s-Sheet 2 Filed May 5, 1956 FIG. 8

//v VENTOR L. R. WRATHALL ATTORNEY Patented May 17, 1938 UNITED STATES PATENT OFFICE HABMONIC PRODUCER New York Application May 5, 1936, Serial No. 77,989

9 Claims.

This invention relates to a generation of alternating current waves, and more particularly to a circuit arrangement for producing a group of harmonic frequencies having a uniformly large amplitude.

Heretofore, it has been found desirable in transmission systems requiring a large number of alternating waves of different frequencies such, for example, as the carrier waves for the several channels of a multiplex carrier telephone, to simultaneously provide the different frequencies by distorting a fundamental frequency of an alternating current wave by use of a single wave distorting device, such, for example, as a thermionic vacuum tube, or a saturating magneticcore coil. From the output of each wave distorting device, the desired harmonic frequencies were selected by suitable circuits, or filters. In the above systems, it is known that the amplitude of the harmonic frequencies decreases very rapidly as the positions of the latter advance in the harmonic scale.

It is an object of this invention to produce from a base frequency wave a group of harmonic frequency waves of more nearly a uniform amplitude distributed over a desired range of frequencies.

In accordance with the invention, the object is attained by employing a particular circuit arrangement in combination with a magnetic-core 3o coil of the unpolarized type. In the preferred embodiment, a fundamental frequency wave impressed on the coil connected in a resonant circuit produces a desired group of odd harmonic frequency waves. An output circuit for the coil 35 includes a condenser connected in series with a load which may be a highly resistive impedance such as a bank of filters. The constants of the output circuit effects in the odd harmonics a uniformly large amplitude distributed over the 4 desired frequency range.

' An additional feature of the invention is a use of a copper-oxide bridge rectifier connected across the output circuit to separate a desired group of even harmonic frequency waves having 45 a uniformly large amplitude distributed over the desired frequency range.

Fig. 1 is a diagrammatic circuit illustrating the preferred embodiment of the invention;

Fig. 2 is a diagrammatic circuit delineating a 0 modification of Fig. l; and

Figs. 3, 4, 5, 6, '7, 8, 9, and 10 are curves showing operating characteristics of the circuits shown in Figs. 1 and 2.

In the preferred embodiment of the invention 55 shown in Fig. 1, an alternating current source l0 generates a fundamental frequency wave, preferably 4 kilocycles, which is impressed on a primary circuit i l comprising in series an inductance Li, a condenser C1, and a non-linear inductance L. The primary circuit II is resonant, or nearly so, to the fundamental frequency wave so that the latter is caused to follow a substantially sine wave form. The inductance L embodying a non-linear magnetic core of a suitable structure such, for example, as the laminated or spiralled tape type produces a desired group of odd harmonics of the fundamental frequency in a well-known manner. The inductance L is preferably formed with a comparatively small diameter so as to provide high magnetizing forces in response to relatively small magnetizing currents thereby enabling an operation within its saturation region. The primary circuit II is designed to obviate reactance to the fundamental frequency and, in addition, to provide a high impedance to the desired range of odd harmonic frequencies. The inductance of L1 is large as compared with that of L.

A secondary, or output circuit [4 comprises a highly resistive impedance load R and condenser C, both of which are connected in series with the inductance L.

To facilitate a description of the operation of the circuit shown in Fig. 1, I1 represents the sinusoidal current flowing at any instant from the alternating source 10 through the primary circuit ii; I: represents the current flowing at any instant in the inductance L; and Ia represents the current flowing at any instant through the output circuit I 4.

The operation of Fig. 1 may be more readily comprehended by following the electromagnetic features of the circuit through one cycle of the fundamental frequency. Accordingly, it is assumed that the current I1 is a sinusoidal wave represented by the equation I1=Io cos pt dB dH 2-}??? volts the inductance is represented by the equation 34.22 d dH X 10' hem-foo and the magnetizing force is represented by the equation where n is the number of turns; and A is the cross-sectional area and d is the mean diameter of the magnetic path. The B-H relationship of the coil is shown in Fig. 4.

Assuming I1 at its maximum positive value in Fig. 3, then the magnetizing force of the inductance L has a value (+)Ho which, as seen in Fig. 4, is larger than the saturating magnetizing force He. At this point, pt=0,

a dt

is substantially zero, and

is very small due to the fact that the value of H is larger than (+)Hs. As I1 decreases but remains above the saturating magnetizing force (+)Hs, the impedance of the inductance L is negligible and consists mainly of the copper loss in its windings. Accordingly, for values of I1 between (+)Ho and (+)Hs a relatively small potential will be developed across the inductance L; 13 flowing in the output circuit M will have a negligible value; and I1 and I will be substantially equal. In Fig. 4, it is seen that a change in H above (+)Hs effects very small changes in B. For the above values of current, the inductance L will have a relatively small value L5 as seen in Fig. 4.

When I1 decreases to a value such that H falls below Hs but remains within the positive and negative saturating magnetizing values, (+)Hs and (--)HB, respectively,

becomes relatively large so that the values of the potential e and the inductance L in the above equations are abruptly increased by the relatively large factors of co and LO, respectively, of Figs. 5 and 6. During this interval,

The current I2 is seen in the broken curve of Fig. 3. As I: decreases below the negative saturation value (--)I-Is,

becomes relatively small so that the values of the voltage 6 and the inductance L decrease abruptly to the comparatively small values shown in Figs. 5 and 6. This terminates the charging of condenser C which then proceeds to discharge through the load R and the inductance L to produce a current I; in the output circuit ll. Due to the relatively small value Ls of the inductance L, the condenser C discharges in the form of an extremely sharp pulse as seen in Fig. 7.

It will be understood that. during the discharge of the condenser C, the inductance L possesses a relatively small impedance so that the I3 pulse is limited largely by the impedance of the load R. As a result, the discharge current rises sharply to its maximum value and then drops sharply toward its minimum value and thereafter decreases in a substantially exponential manner until the charge on condenser C is entirely dissipated. At this time, the current In is again substantially equal to the current I1 as seen in Fig. 3. The above action is then repeated in the opposite direction during which I1 attains values whereby the inductance L is caused to.

manifest a change in value. As a consequence thereof, the aforementioned values of I2 and I; are repeated in the opposite direction, as shown in Figs. 3 and 7.

The sharp pulse of Is resulting from the discharge of the condenser 0 effects a uniformly large amplitude in the desired group of odd harmonies produced, as hereinbefore described, in the load R. The form of the I3 curve is determined by the values of the impedance R and the condenser C of the output circuit, and also by the relatively small inductance of L during the discharge interval of the condenser C. These values may be preselected to provide a desired performance or constant, of the circuit.

Referring to Fig. '7, the curve of current I3 indicates the following; first, that during each I1 cycle, the current I3 is divided into two isolated pulses in a manner that relatively small values of Is are interposed therebetween; and second, that each pulse is sharply divided into two stages. In connection with the latter, the first stage, pt1 to 11132, resembles a slow growth of current in response to a potential impressed on a circuit containing a relatively large inductance; and the second stage, 13152 to 1r+Pt1 resembles the discharge of a condenser through a relatively small inductance and a resistance.

The non-linear inductance L may also be considered as having two distinct values of inductance, one for each of the two stages of Is extending from M1 to 1r+pt1 in Fig. '7. As seen previously, one of the inductances is relatively smaller than the other. Therefore, the smaller value of inductance must be so small that the fundamental potential impressed thereacross would be negligibly small to account for the absence of an appreciable steady-state fundamental current during this time. In addition, the dincharge of condenser C must be sharply effected to account for the negligible portion of I: flowing during this interval.

Accordingly, it is seen in Fig. 7 that for each sharp pulse of Is, the condenser C is charged and discharged in less than a half-cycle of the fundamental current wave.

The larger value Lo would seem to be associated with the initial permeability of the magnetic core of the inductance L while the value Ls would seem to be associated with the saturation permeability of the magnetic core.

Figs. 8 and 9 are oscillographic representations of the currents I2 and I3, respectively, obtained by a circuit similar to the circuit described above.

Fig. 2 is a modification of the circuit shown in monics both of which may be used for cable car' rier and coaxial channel terminals. The output circuit of Fig. 2 is connected to the primary winding of a transformer 34 having its secondary winding connected to a bank of filters 35 comprising six in number (by way of example) and arranged for parallel operation to pass only the desired group of odd harmonics. To provide a desired group of even harmonic frequencies, there is employed a copper-oxide bridge rectifier 36 comprising one pair of the conjugate bridge terminals connected across the secondary circuit 30 and a second pair of output bridge terminals connected to the primary winding of a transformer 31. The secondary winding of the latter is connected to a bank of filters 38 comprising six in number and arranged for parallel operation to pass only the desired groups of even harmonic frequencies.

The arms of the rectifying bridge are so poled that alternate pulses of I; are reversed thereby causing current to always flow in the same direction through the primary winding of the transformer 31. As a consequence thereof, only the even harmonics are provided with a uniformly large amplitude distributed over a desired frequency range.

When the banks of filters 35 and 38 cover a wide range of harmonic frequencies so as to provide a substantially uniform impedance, the operation of the secondary circuit 30 of Fig. 2 approximates closely the operation of the resistive secondary circuit l4, therefore the form of I: effected by the output current 30 of Fig. 2 would be substantially identical with the form of I: effected by the circuit of Fig. 1 as shown in Fig. 9. Accordingly, a uniformly large amplitude distributed over the desired frequency range of the produced odd harmonics would be effected in the output circuit of Fig. 2.

When the operation of secondary circuit 30 tends to vary substantially from the above, one of the following adiustments thereto may be adopted; first, the banks of filters may be flanked by highand low-pass filters so as to provide a sufficiently uniform impedance over the entire desired frequency range; second, a condenser may be shunted across either transformer 34 or 31, or both; and third, a transformer having a sufliciently large shunt capacity associated with its winding may be substituted for either transformer 34 or 31. It will be observed, however, that a use of the above shunting elements alters the form of I; so as to include an extra loop as illustrated in Fig. 10, and, in addition, that the distribution of 13 remains uniform although the amplitude of the produced harmonics is slightly increased Fig. 10 is an oscillographic record made from an output circuit embodying the above shunting elements.

It is to be understood that the invention is capable of other modifications by those skilled in the art, and is to be limited only by the scope of the appended claims.

What is claimed is:

1. A harmonic producing circuit comprising an alternating current generator of fundamental frequency, a circuit connected across the generator and comprising in series an air-core induction coil, a capacity, and an induction coil having a saturable magnetic core tuned to the fundamental frequency; the magnetic-core coil producing a desired group of odd harmonics of the fundamental frequency and the inductance of the air-core coil being large compared with the inductance of the magnetic-core coil, and an output circuit for effecting a uniformly large amplitude in the produced harmonics comprising a second capacity and a highly resistive load circuit connected in series with the magnetic-core coil.

2. A harmonic producing system comprising an induction coil having a saturable magnetic core, means for impressing sufficient alternating current energy of a base frequency on the coil to cause saturation of its core so as to produce odd harmonics of the base frequency in the coil, and an output circuit for the coil including means for making certain that the produced harmonics will have a uniformly large amplitude over a desired frequency range, the means in the output circuit comprising a capacity and resistance in series with the induction coil, said resistance being sufficiently high to render said output circuit non-oscillatory within the range of utilized harmonics.

3. A harmonic producing circuit comprising a the first-mentioned coil comprising a capacity and a load in series therewith, the values of the second-mentioned capacity, the effective resistance of the load, and the smallest inductance of the first-mentioned coil being so chosen as to make the output circuit substantially aperiodic whereby harmonics are produced within a desired frequency range of a uniformly large amplitude; and means associated with the output circuit for selecting certain of the harmonics within the desired frequency range.

4. A harmonic producing system comprising an induction coil having a saturable magnetic core, means for impressing alternating current energy of a fundamental frequency on the coil to produce odd harmonics of the fundamental frequency therein, an output circuit for the coil comprising a capacity in series with a highly resistive impedance; the values of the capacity,the impedance and the smallest inductance of the coil being selected to make the harmonics within a given frequency band of a uniformly large amplitude; and means in the output circuit for se- -lecting certain of the odd harmonics in the desired frequency range.

5. In a system for producing harmonics, an induction coil having a saturable magnetic core, means for impressing alternating current energy of a fundamental frequency on the coil to cause saturation of its core so as to produce a desired group of odd harmonics of the fundamental frequency on the coil, an output circuit for the coil comprising a capacity and resistance in series therewith, the total resistance being sufficiently large to confine the condenser discharge current principally to a single short sharp impulse in each half cycle of the fundamental wave to cause the generated odd harmonics to have a uniformly large amplitude distributed over the desired frequency range, said total resistance including a copper-oxide rectifier bridge connected across the output circuit for rectifying a portion of the odd harmonic energy, and a circuit connected across the conjugate points of the bridge for taking off even harmonics of the fundamental frequency.

6. In a system for producing harmonics, an induction coil having a saturable magnetic core, means for impressing alternating current energy of a fundamental frequency on the coil to cause saturation of its core so as to produce odd harmonics of the fundamental frequency in the coil, an output circuit for the coil comprising a capacity in series with a highly resistive impedance; the values of the capacity, the impedance, and the smallest inductance of the induction coil being selected to confine the condenser discharge current principally to a single short sharp impulse in each half cycle of the fundamental wave to effect a uniformly large amplitude in the generated odd harmonics distributed over the desired frequency range; means connected across the output circuit for selecting certain of the odd harmonics in the desired frequency range, a copper-oxide rectifier bridge connected across the output circuit for rectifying a portion of the odd harmonic energy, and a circuit connected across the conjugate points of the bridge for taking off even harmonics of the fundamental frequency, said copper oxide rectifier comprising a part of the highly resistive impedance of the output circuit.

7. In a system for producing harmonics, an alternating current generator, an induction coil having a saturable magnetic core, a circuit coupling the generator across the coil and including an air-core induction coil and a capacity in series therewith, the circuit being tuned to the fundamental frequency of the generator for producing odd harmonics of the fundamental frequency in the magnetic-core coil, the inductance of the aircore coil being relatively large as compared with the inductance of the magnetic-core coil, a loar. circuit including a capacity connected across the magnetic-core coil; the value of the last-mentioned capacity, the effective resistance of th.

load circuit, and the smallest inductance of the magnetic-core coil being selected to confine the condenser discharge current principally to a single short sharp impulse in each half cycle of the fundamental wave to effect over the desired frequency range a uniformly large amplitude in the produced odd harmonics; means connected across the load circuit for selecting certain of the odd harmonics within the desired frequency range, a copper-oxide rectifier bridge connected across the output circuit for rectifying a portion of the odd harmonic energy, and a circuit con-' nected across the conjugate points of the bridge for taking off even harmonics of the fundamental frequency, said copper oxide rectifier comprising a part of the highly resistive impedance of the output circuit.

8. In combination, a saturable core inductance, an exciting circuit producing substantially sinusoidal current flow through said inductance of sufficient amplitude to produce saturation in said core, and an output circuit including in series a winding on said core and a condenser and a highly resistive load, said output circuit containing sufficient resistance to render it substantially aperiodic whereby a broad range of harmonic frequency currents are produced in said load.

9. A harmonic frequency producing system comprising a saturable core inductance, a circuit for applying base frequency current thereto of sufiicient amplitude to saturate said core, an output circuit connected across a winding on said core and including a condenser and a highly resistive load in series, the time constant of said output circuit being proportioned to permit said condenser to become substantially fully charged during the portion of the cycle throughout which said inductance has its maximum value and to discharge through said load when said inductance has substantially its minimum value, the resistance of said output circuit being so high as to render the output circuit highly damped.

LEISHMAN R. WRATHALL. 

